Alaska’s sea otters are helping to combat ocean acidification by preying on sea urchins which, if left unchecked, could be detrimental to the health of the oceans, according to a new study.

Sea otter grooming among kelp

Climate-friendly lunch

By preying on sea urchins that feed on underwater kelp beds, sea otters are stemming the accumulation of acidic carbon dioxide in Alaska’s waters. When absorbed into the ocean, atmospheric carbon dioxide increases water acidity levels, a phenomenon known as ‘ocean acidification’, which can be harmful to marine environments. Kelp beds are important components of marine ecosystems, as they absorb oceanic carbon dioxide during photosynthesis, and produce oxygen in its place.

According to a new study published in a recent issue of Frontiers in Ecology and the Environment, otter-protected kelp beds absorb approximately 12 times as much carbon dioxide during the process of photosynthesis as thinned-out kelp beds. By eating sea urchins, otters are providing the kelp forests with a chance to grow and help reduce ocean acidification.

Based on prices used in the European Carbon Exchange, the study reports that it would cost between $205 million and $408 million to offset the carbon that urchin-eating sea otters are enabling kelp beds to absorb.

Sea otter feeding on red sea urchin

Cute and beneficial

Co-author Jim Estes said that he hopes the study, which relied on data collected over a 40-year period between British Columbia, Canada, and Alaska’s Aleutian Islands, would help people to understand the importance of sea otters and the far-reaching benefits they provide.

“On the one side, people like sea otters because they’re fuzzy, cool things. On the other side, a lot of people hate them,” said Mr Estes, a biologist and sea otter expert at the University of California, Santa Cruz. He went on to explain that fishermen, including shellfish harvesters, are in direct competition with sea otters, and are notoriously hostile towards the charismatic marine mammals. However, Mr Estes pointed out that by preserving kelp forests, sea otters are actually providing a service to fishermen, as kelp beds are an important habitat for many fish species.

Sea otter pair anchored in kelp

A species under threat

Victims of a commercial harvest, sea otters were once hunted to the brink of extinction, until a treaty in 1911 ended the commercial hunt and numbers began to increase. Yet according to the U.S. Fish and Wildlife Service, the species is still not out of the woods. The sea otter population from Kodiak, Alaska, to the western Aleutian Islands has dropped sharply in size in recent years, potentially declining as much as 67% since the mid-1980s. In 2005, the western Alaska sea otter population was listed as ‘threatened’ under the Endangered Species Act.

Oil spills and other human-related impacts have also had a negative effect on sea otter numbers, but many scientists studying Alaska’s populations believe that predation by killer whales is currently the main reason for declines. Steller’s sea lions and seals, key prey species for killer whales, have become scarce, leading the whales to target sea otters.